i have your exact same problem since more than 12 years, been seeing many doctors most of them was a waste of time but i got some theories about the whole thing..definitely could use a chat with someone in my same shoes. anyhow check out "animus", "rectal prolapse" and see if you relate with the symptoms and diagnosis; my theory is that when i have bowel movement some of the stool remains trapped in the rectum and this causes the smell